1. Field of the Invention
The present invention relates to a construction anchor, and more particularly to a construction anchor receivable in a hole defined in structural materials, such as masonry, concrete, wood or metal, to secure an object or fixture to the surface of the structural material.
2. Description of the Prior Art
Construction anchors of the above-mentioned general type are known in the art. Typically, such anchors are made of metal in a substantially cylindrical shape. They also include a longitudinal threaded bore in which an appropriately sized, headed bolt may be disposed.
In use, construction anchors of this general type are adhesively bonded into holes defined in masonry, concrete and similar materials. When the cement or adhesive, perhaps an epoxy, has sufficiently hardened or cured, an object may be mounted on the masonry surface by means of a bolt driven into the threaded bore of the construction anchor.
In the prior art, it has proven to be difficult to set the construction anchors to a uniform depth in the holes drilled in the structural material. In addition, as the cement or adhesive is introduced into the hole before the construction anchor, it has a tendency to be forced out of the hole as the construction anchor is being introduced thereinto, and to exude or seep into the threaded bore, where it may harden and prevent a bolt from being readily disposed therein. The introduction of dust and dirt into the threaded bore causes similar problems.
U.S. Pat. No. 5,263,804 shows a construction anchor which represents a solution to these deficiencies of the prior art. The construction anchor includes a metal anchoring portion and a plastic cap. The cap has a flange which is of a larger diameter than that of the hole in which it is to be inserted, so that the anchor may be seated in the hole to an optimum depth. The cap also has a plurality of longitudinal raised ridges spaced circumferentially thereabout, so that the anchor may be centered in the hole. The metal anchoring portion, in addition to including a threaded bore, has at least one annular groove defining a conically shaped lobe at the end thereof opposite to that having the threaded bore. The anchor is adapted to be inserted, metal anchoring portion first, into a pre-drilled adhesive-filled hole. When the adhesive has set, a screw or bolt is inserted through the top of the plastic cap to engage the threads in the threaded bore. The conically shaped lobe inhibits the removal of the anchor from the hole, once the adhesive has hardened, by wedging the adhesive against the hole walls when forces tending to extract the anchor from the hole act thereupon.
The cap of the anchor shown in U.S. Pat. No. 5,263,804 has a preselected longitudinal length which provides a stretch zone for a screw or bolt disposed in the threaded bore. The stretch zone enables the screw or bolt to withstand dynamic cyclical loading or vibration forces, as the initial stress placed thereon during tightening tends to elongate the screw or bolt, enabling either to overcome "creep" at peak dynamic cyclical loading or the effects of vibration induced by wind or other forces. The length of the cap also provides space for the "fingers" which are bent inward from the center portion of the top thereof when a screw or bolt is pushed and enters therethrough.
In practice, the use of the cap to provide the stretch zone has led to problems, because the cap does not provide any lateral support to the screw or bolt. Without lateral support, the screw or bolt may bend and snap in response to shear forces. As a consequence, the need for an improvement upon the anchor shown in U.S. Pat. No. 5,263,804 has arisen. The present invention provides such an improvement.